Dissolving and solubility Section 6.2

Objectives Describe how a substance dissolves in terms of its solubility, molecular motion, and solute-solvent interactions. Identify several factors that affect the rate at which a substance dissolves. Relate the structure of water to its ability to dissolve many different substances. Distinguish between saturated, unsaturated, and supersaturated solutions.

The dissolving process Solutes with a ___________________ dissolve faster. A substance in small pieces will dissolve faster than the same substance in larger pieces. The more surface area, the more solute-solvent interaction there will be. Example: __________ vs___________, chewing a vitamin vs. swallowing it whole

The dissolving process ___________________a solution helps the solute dissolve faster Stirring or shaking creates more interaction between the solute and the solvent. Solutes dissolve faster when the solvent is _______. When the solvent is warmer, its molecules move faster which creates more collisions between solute and solvent particles.

The dissolving process Not every substance dissolves Substances that dissolve in another substance are ___________ in that substance. Some substances will not dissolve in other substances and are _____________.

Water: a common solvent ___________________________________ _________. Water is a polar molecule – meaning its electrons are not evenly spread through the molecule. Oxygen has a partial negative charge and both hydrogens have a partial positive charge See Figure 6-12 on pg 195 to see why salt dissolves easily in water.

Water: a common solvent The ______ are attracted to water molecules which pulls them away from the solid. Substances made of molecules that dissolve in water have charges that interact with water molecules. They exist as molecules, not ions, though.

Water: a common solvent ____________________ Polar substances will dissolve in other polar substances Example: methanol dissolves in water Non-polar substances will dissolve in other non-polar substances Example: gasoline in oils

concentration Solutions can have different concentrations Depends on how much solute and solvent there are If there is a small amount of solute in a large volume of solvent, it is _________. A _______________ solution has a large amount of dissolved solute.

concentration ___________________ can dissolve more solute. They have more _________ molecules than solute molecules. It is _______________ as long as solute can continue to be dissolved.

concentration At some point, most solutions become saturated with solute. If you add more solute, ______________ __________________. How much solute will dissolve depends on the solute’s __________ and the solvent’s _____________.

concentration __________ a saturated solution usually allows you to dissolve even more solute. The amount of solute that dissolves in a solvent __________ as temperature increases. It will keep dissolving until it is saturated at the higher temperature. When the _______________ solution cools down, it is holding more solute than it normally can.

concentration Adding a small crystal gives a surface for the excess solute to start crystallizing This will continue until it reaches its normal saturation at the cooler temperature.

concentration Measuring concentration precisely Concentration can be expressed in units of ___________. Molarity = OR M = Moles of solute Liters of solution mol L

Section 6.2 summary The larger the surface area a solute has, the faster it will dissolve. Stirring or shaking the solution dissolves the solute faster. Heating a solvent also dissolves solutes faster. So many substances are soluble in water that it is sometimes call the universal solvent. An unsaturated solution can dissolve more solute. A saturated solution cannot dissolve any more solute. A solute’s solubility is exceeded in a supersaturated solution.